Variable resistors and potentiometers



Dec. 2, 1958 v. A. w. PAGE 2,863,030

VARIABLE RESISTORS AND POTENTIOMETERS Filed Feb. 4, 1957 2 Sheets-Sheetl 5 I 4 I Fla.

Dec. 2, 1958 v. A. w. PAGE 2,863,030

VARIABLE RESISTORS AND POTENTIOMETERS Filed Feb. 4, 1957 2 SheetsSheet 2United States Patent VARIABLE RESISTORS AND POTENTIOMETERS Victor ArthurWilliam Page, Rockley, Marlborough, England, assignor to The PlesseyCompany Limited, Ilford, England, a British company Application February4, 1957, Serial No. 655,456

Claims priority, application Great Britain February 16, 1956 Claims.(Cl. 20155) This invention relates to variable resistors andpotentiometers and provides an improved construction in which theelectrically operative elements are combined in a self-containedsub-assembly ready for the insertion of an actuating spindle.

According to one aspect of the invention the resistor or potentiometercomprises a base or stator element, in one face of which a circular orpart-circular resistance track and a circular or part-circular contactring or ring segment are arranged substantially concentrically around acentral guide bore extending through the base. A movable contactelement, adapted to connect selected point of the resistance track withthe contact ring or segment, is rotatable by a bush member extendingthrough and journalled in the guide bore of the base, and is securedagainst axial movement out of said bore by a self-locking clip device orother locking member at the back of the base, and preloaded resilientmeans acting axially between the face of the resistance track andcontact ring or segment and the bush member are provided for maintainingthe bush member in the axial position determined by the locking member.These resilient means maintain a predetermined contact pressure betweenthe contact element and the resistance track and contact ring orsegment. The bush member has an axial bore for the insertion of anoperating shaft or other operating member and means for coupling thehush with said shaft, or the like, for common rotation. These couplingmeans are preferably so constructed that they freely allow axialmovement of the spindle relative to the bush.

It is a particular advantage of this construction that the contactpressure is determined before the operating spindle is inserted and willnot be affected by the assembly with the spindle thus eliminating ahitherto unavoidable factor of uncertainty in the electricalcharacteristics. Inaccuracy in the length of the actuating spindle willtherefore not effect the electrical characteristics of a resistor orpotentiometer according to the invention.

The accompanying drawings illustrate the invention Fig. 1 is anelevation, partly in section, of the subassembly containing theelectrically operative elements,

Fig. 2 is an underneath plan view,

Fig. 3 is a sectional elevation showing a complete resistor orpotentiometer,

Fig. 4 similarly shows two resistors or potentiometers actuated by acommon shaft for ganged control,

Fig. 5 shows two resistors or potentiometers arranged similarly forindividual adjustment by coaxial shafts, and

Fig. 6 shows a simplified complete resistor or potentiometer suitablefor use in preset circuits.

Referring now first to Figs. 1 to 3, a base or stator element 1 made ofinsulating material, for example of a phenol-formaldehyde plastic,carries on one of its faces a part-annular resistance track 2 and,concentric therewith a contact ring 3, both accommodated in suitablegroove-like recesses. A movable contact element for co-operation withthe track 2 and contact ring 3 is constituted by a resilient contactcarrier 4, which is equipped with contact brushes 5 and 6 respectivelyengaging the tracks 2 and 3. A hub member or bush 7 extending throughand guided in a central cylindrical aperture 8 of the base 1 is providedwith a flange 9 which faces the tracks 2 and 3 in spaced relation. Thecontact carrier 4'is located relative to the bush 7, so as to maintainthe brushes 5 and 6 in respective engagement with the tracks 2 and 3, byan eccentric portion 19 of the bush and by being formed at diametricallyopposite .points with upwardly (with reference to Fig. 1) decesses 11 ofthe flange 9, thus coupling the contact carrier with the hub for commonrotation; the curved back of the contact carrier is supported againstthe flange 9, so that its resilience in conjunction with the spacingbetween this flange and the base 1 determines the contact pressure bywhich the brushes 5 and 6 are applied to the tracks 2 and 3. Thisspacing is determined by a stop in the form of washer 12 of resilientmetal provided with internally projecting tongues 13 which are deflectedor, since preferably a washer having pre-bent teeth is employed, furtherdeflected as the washer is forced onto the bush 7. This sliding-onmovement is limited by the abutment of the end face 20 of eccentric bushportion 19 against the face of the base 1 or contact ring 3. A plainmetal washer 14 is preferably inter posed between the washer 12 and theback of the base 1 An axially projecting lug 15 suitable for theoperation of an on/off switch and a radially projecting stop lug 16 maybe provided at the back of the flange 9 as shown.

The base 1 is provided with electric terminal strips 21 and 22respectively connected to the two ends of the resistance track 2 and afurther terminal strip 23 connected to contact track 3.

The bore 17 of the bush 7 is preferably a through bore as shown in Fig.3, provided with internally projecting axially extending coupling ribs,for example in form of serrations 18 extending from the back surface ofthe flange 9 through about half the length of the bush 7.

The sub-assembly just described comprises all those elements whichaffect the electrical characteristics of a complete variable resistor orpotentiometer. It has the advantage over known devices that it can becombined with an actuating shaft in such manner that the applicationpressure of the contact members 5, 6 is not affected by movement of theshaft relative to the base, and that therefore considerable tolerancesin the length of the shaft are permissible.

Fig. 3 shows a complete resistor suitable for singlehole fixing in aradio chassis, incorporating this subassembly. A shaft 24, which has afluted end portion 25 slidably fitting into the serrated part 18 of thebore 17, is journalled in the mounting bush 26 of a housing base 27, twospring rings 28 being provided for locating it axially. The circularrear portion 29 of the base 1 fits into a recessed step 30 of thehousing base 27, and a housing cap 31, having two clip arms 32 extendinglongitudinally and accommodated in suitable notches 33 (Fig. 2) in thecircumference of base 1 and housing base 27, complete the assembly.

Fig. 4 shows a similar arrangement, in which however two sub-assemblies,each as shown in Figs. 1 and 2, are mounted on a common shaft 24a. Asshown, each unit may be enclosed in a separate housing, the cap 31a ofthe housing for the inner unit having a hole through which the shaft canpass, and carrying a light housing base 27a for the outer unit. Theshaft 24:; has a fluted portion 25a which extends from the serrated partof the bush of the inner unit through the Whole length of the bush 7 ofthe outer unit.

In the embodiment of Fig; 5 the two units are similarly arranged andhoused,.but the shaft 24b of the inner unit is bored longitudinally toaccommodate rotatably a reduced-diameter'spindle part 124a of a secondshaft 112 for the actuation of the outer unit.

Fig. 6 illustrates a very simple embodiment, it particularly intendedfor use as. a pre-set resistor o k I tentiometer. The shaft isconstituted by a plug integral with a moulded-plastic setting knob whichextends through a hole in the housing cap 310. if the knob is made-ofreasonably soft plastic, for example polythene, and the bush member ofhard plastic, for example a phenolic-resin composition, it is notnecessary for the plug 34 to be'fluted in manufacture, since theserrations 18 will bite into the surface of the plug when the same isforced into the bore of the bush. The knob 35 may be provided With aflange or car 36 which is held captive between the housing cap 31c andthe flange Z of the bush '7. The housing cap 31c has screw-threadedbosses 37, by which it can be attached to the back of a panel or likewall.

What is claimed is:

1. A variable resistor device, comprising a base member of insulatingmaterial having two parallel surfaces, a guide bore extendingtherethrough to interconnect said surfaces, and a resistor track and acontact track both arranged at one of' said surfaces, substantiallyconcentrically with said bore, a bush of insulating material extendingthrough said here and having an end projecting from the surfacecontaining said tracks, said end being formed with a circumferentialshoulder in contact with said surface and with an abutment flange spacedfrom said surface and extending radially yond said shoulder, a movablecontact element rotatably guided on said bush between said shoulder andsaid abutment flange and having two contact points and a support point,said contact points respectively resting on said contact track and onsaid resistance track, and said support point resting against saidabutment flange and being resiliently movable axially of the bushtowards and away from said contact points, and a thrust collarco-operating with the other said surface of the base member and havingresilient locking legs extending from said collar into resilientself-locking engagement with said bush outside the base member adjacentsaid other surface thereof.

2. A device as claimed in claims 1, wherein a metal washer is interposedbetween the thrust collar and the base member.

3. A device as claimed in claim 1, further comprising a housing member,located on the circumference of the base member.

4. A device as claimed in claim 3, wherein said housing member includesan inwardly projecting stop and the abutment flange of the insulatingbush is provided with a projection co-operating with said stop forlimiting the rotation of said bush in the guide bore.

5. A device as claimed in claim 1, further comprising a bearing memberhaving locating means co-operating with the circumference of the basemember for ensuring alignment of saidbearing member with the bore of thebase member.

References (Jilted in the file of this patent UNITED STATES PATENTS1,356,634 Koch Oct. 26, 1920 1,624,038 Carter Apr. 12, 1927 1,773,609Yoshiyasu Aug. 19, 1930 2,145,953 Schellenger Feb. 7, 1939 2,401,037Arvin May 28, 1946

